Marketable Securities - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Fixed Income Securities	$ 832,000		$ 832,000		$ 5,300,000
Purchases of marketable securities			405,000	$ 18,876,000
Proceeds from sales of marketable securities			4,896,000	16,319,000
Realized gains on sale of marketable securities	3,000	$ (2,000)	12,000	(9,000)
Unrealized holding gain (loss) arising during the period	$ 1,000	$ (7,000)	$ 6,000	$ (1,000)
Marketable securities, effective maturity period (in years)			9 months 18 days
Marketable securities, average effective duration (in years)			1 month 21 days